Filter provided with structural elements, in particular for a rotary separator

ABSTRACT

A filtering body, in particular for a rotary separator, extends about an axis and has a two opposite axial faces, a radially outer surface and a radially inner surface; the filtering body comprises a filtering net constituted by filaments defining a plurality of pores between them; a frame, which is defined by non-porous solid elements, supports the filtering net and made in one piece with a filtering net; the frame has at least one element arranged in an intermediate radial position between the radially outer and inner surfaces.

The present invention relates to a filter provided with structuralelements, in particular for a rotary air/oil separator in a turbineengine.

BACKGROUND OF THE INVENTION

As known, in aeronautic turbine engines, the oil used for lubricatingthe bearings and cooling the transmission tends to mix with air.However, the used oil must be retrieved and re-introduced into thehydraulic circuit of the engine, in order to limit consumption andreduce the polluting substances discharged into the atmosphere. Variousdevices, either of the static type, named cyclones, or of the rotatingtype, named rotary separators or deoilers, may be used in order toseparate the oil from the air. The latter are generally defined bymetallic filtering nets.

Both devices are usually used, to separate oil particles havingdiameters in very different dimensional ranges. Commonly, cyclonedevices are used to separate the larger sized oil drops suspended in airand degassing the larger air bubbles suspended in oil from the oil.Cyclone technology, in all cases, cannot separate the smaller oil dropsand the smaller air bubbles. In general, the smaller air bubblesdissolved in the oil do not generate major drawbacks. The smaller oildrops, on the other hand, are separated and collected by means of arotary separator arranged after the cyclone device along the air-oilmixture flow path.

The rotary separator comprises a toroidal-shaped filter, which is fittedon a rotor and has a pack of annular bodies each defined by a respectivemetallic filtering net. The filter, on a face thereof, receives theintroduced air-oil mixture, lets through the air towards the rotor axisand withholds the oil particles in the pores of the metallic filteringnet.

In the metallic filtering net, the rotation has the double function of:

-   -   increasing the number of potential collisions of the oil drops        against the filtering elements of the net, determining oil        coalescence in form of film, which covers such filtering        elements;    -   centrifuging the oil film towards the outer periphery of the        filter so as to retrieve such oil.

Using a rotary separator causes an additional pressure loss in thecompressed air system of the turbine engine. Such an aspect becomesparticularly critical when the revolution speed of the engine, and thusof the compressor, is relatively low. Indeed, in such operatingconditions (idle or taxi conditions) the air pressure in the bearingseals will also be low, with consequent incapacity to maintain sealingif the metallic filter net causes an excessive back pressure. Themetallic filtering net structure must be designed in extremely carefulmanner to obtain a correct trade-off between pressure loss andseparation efficiency.

Patent application having publication number EP2156941A1, in the name ofthe same applicant, and other documents of the prior art teach tomanufacture filtering bodies by means of layer by layer or additivemanufacturing techniques, which employ an energy beam, i.e. a focusedelectron beam or a focused laser light beam, to obtain the localizedmelting and/or sintering of subsequent layers of powders having the samecomposition as the end product to be obtained. The zones to be meltedare established by means of a three-dimensional numerical model whichrepresents the product to be made and which is stored in an electronicunit configured so as to control the energy beam.

These techniques are known, for example, as Direct Laser Forming (DLF),Laser Engineered Net Shaping (LENS), Direct Metal Laser Sintering(DMLS), Selective Laser Melting (SLM), or Electron Beam Melting (EBM).

In the techniques in which sintering is required, the energy beam heatsthe outer surface of the powder grains so as to melt only such outersurface which joins with that of the adjacent grains. In this manner,the pores of the filter are defined by the gaps between the powdergrains joined to one another.

Patent application EP2156941A1, on the other hand, relates to atechnique requiring the melting of the powders: the powders have smallergranulometry than those used for sintering and their grains arecompletely melted. The pores of the filter are defined by the powderparts which are not concerned by the energy beam. Thus, thethree-dimensional numerical model represents not only the outer shape ofthe filtering net but also its inner porous structure.

In particular, the three-dimensional model is generated by defining abase module, which represents a cell of the filtering net, and byreplicating the same base module again and again until the shape anddimensions corresponding, in the three-dimensional model, to those ofthe filtering body to be made are reached. Document EP2156941A1indicates making a porous cell structure of the diamond structure kindor honeycomb kind.

Thus, the method described in EP2156941A1 allows to define the geometryof the metallic filtering net to obtain the desired porosity of thefilter in relatively accurate manner, also as a function of thedifferent zones of the filter and as a function of the pressure losscaused by the rotary separator as a whole. Furthermore, it allows tomake the porous structure of the filtering net uniform, and thus tobalance the effects of the centrifuge force and position the centre ofgravity of the filter exactly on the rotor axis.

Additionally, EP2156941A1 teaches to provide three-dimensional numeralmodels which integrate, together with the filtering net, solid materialelements arranged along the outer edges of the filter, so as to havestructure element which support the filtering net and thus reinforce thefilter.

The need is felt to improve the known solutions described above, inorder to maximize the oil capturing efficacy and to limit, at the sametime, the back pressure in the compressed air system of the turbineengine.

SUMMARY OF THE INVENTION

It is the object of the present invention to make a filter provided withstructural elements, in particular for a rotary separator, which allowsto simply and cost-effectively meet the aforementioned need.

According to the present invention, a filtering body, in particular fora rotary separator, is made.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the present invention, a preferredembodiment will now be described by way of non-limitative example onlyand with reference to the accompanying drawings, in which:

FIG. 1 is a section view which shows, in simplified manner, a rotaryair/oil separator in a turbine engine, with a preferred embodiment ofthe filtering body according to the present invention;

FIG. 2 is a diagrammatic cross-section on enlarged scale of thefiltering net of the filtering body in FIG. 1, taken along a sectionplane which is orthogonal to elongated filtering elements belonging tosuch a filtering net;

FIGS. 3 and 4 are similar to FIG. 2 and show respective examples of howthe filtering net can be obtained by replicating a base cell;

FIGS. 5a-5c show respective configurations of the filtering elements inFIG. 2;

FIG. 6 shows a diagrammatic cross-section of the filtering body in FIG.1;

FIG. 7 shows a variant of FIG. 6 on enlarged scale; and

FIGS. 8 and 9 are perspective views of the filtering body in FIG. 6,with parts removed for clarity to highlight structural elements of thedisc itself.

DETAILED DESCRIPTION OF THE INVENTION

In FIG. 1, reference numeral 1 indicates a rotary air/oil separator in aturbine engine.

The separator 1 comprises a casing 2 defining an inner chamber 3 havingan inlet 4, from which a mixture of air and oil enters, in directionsubstantially tangential with respect to an axis 5. Furthermore, theseparator 1 comprises a rotor 6 (partially shown), which extends alongthe axis 5 in the chamber 3, is rotatably fed about the axis 5 (inmanner not shown) and internally defines an axial cavity 7,communicating with an outlet (not shown) for discharging air.

The separator 1 further comprises a filter 8, which is accommodated inthe chamber 3, is supported by the rotor 6 in fixed coaxial position, istoroidal and comprises a plurality of annular filtering bodies. Suchbodies are indicated by reference numeral 10, generally named “discs”,are coaxial, axially rest against one another and are restrained to oneanother by means of driving pins or fastening pins (not shown) forcoupling and transmitting the rotation torque.

In FIG. 1, the filter 8 comprises a cage 11, which supports and containsthe discs 10 and is shaped so as to leave open an axial inlet for themixture, an outer radial outlet for the oil and a radial inner outletfor the air. However, according to variants (not shown), the cage 11could be absent and/or the filter 8 could comprise a single disc 10.

Preferably, the oil and air phases of the mixture undergo a first roughseparation in chamber 3. The mixture enters the filter 8 frontally byeffect of the pressure difference between the chamber 3 and the axialcavity 7. Considering a single disc 10 of the filter 8 (shown partiallyand in cross-section in FIG. 6), the mixture enters through an axialface 11 a and/or through an outer cylindrical surface 12 of the disc 10.The oil exits through the surface 12, and the air exits through acylindrical inner surface of the disc 10. The disc 10 has a face 11 b,also permeable to the mixture, from the opposite side of the face 11 a.

The discs 10 comprise respective filtering nets 14, defining porousstructures which separate the two phases of the mixture. In particular,the rotation of the filter 8:

-   -   increases the number of potential collisions of the oil drops        with the elements or filaments of the filtering nets 14 (as will        be explained again below) and thus determines the coalescence of        the oil inside the pores, e.g. in form of film which covers such        elements or filaments;    -   centrifuges the oil captured in the pores and expels it outwards        by effect of the inertia of the oil itself.

Again with reference to FIG. 1, the centrifuged oil exits through thesurface 12, as mentioned above, and deposits on a portion 16 of thecasing 12. The portion 16 has an outlet 17, through which the oil flowsto be collected in a tank (not shown) belonging to a hydraulic circuitof the turbine engine.

At the same time, the air flows into the axial cavity 7 through someradial openings 18 made in the rotor 6, and the axial cavity 7 is thendischarged off-board into the atmosphere.

Reference will be made to only one of the discs 10 for the sake ofsimplicity in the following description, because the discs 10 aresubstantially equal to one another. Preferably, as shown in thediametric cross-section in FIG. 6 and will be described in detail below,the disc 10 comprises a frame 20, which is constituted by solid (i.e.non-porous) structural elements and is integral with the filtering net14 (i.e. made in one piece with the filtering net 14) so as to supportthe elements or filaments of the filtering net 14.

The material of the disc 10 is metallic and defined, for example, by atitanium alloy or a nickel-chromium alloy.

The forming method and the machine for manufacturing the disc 10correspond to the indications of patent application EP2156941A1, thedescription of which is incorporated here at least for the partsnecessary to understand and carry out the present invention.

In brief, the disc 10 is made by means of layer by layer or additivemanufacturing techniques which employ an energy beam, e.g. a focusedelectron beam or a focused laser beam, to melt subsequent layers ofpowder having the same composition as the end product to obtain inlocalized manner. In general, the powders have a granulometry comprisedin the range from 20 to 150 μm.

The scanning of the energy beam on each layer of powder is controlled byan electronic control unit in which a three-dimensional numerical modelis stored. Such a model represents the desired shape, dimensions andporous inner structure of the disc 10, and may be generated, forexample, by means of a computer assisted design (CAD) software. Eachlayer of powders is melted in localized zones, which are selected by theelectronic control unit on the basis of the three-dimensional numericalmodel data. For each layer, the melted part “amalgamates” with thepreviously formed part underneath belonging to the previous layer.Progressively, layer by layer the height of the product increases toobtain the end finished product. Residual powder grains remain in thezones which are not melted in each layer. The spaces occupied by such aresidual powder are freed at the end of the forming method and definethe pores of the filtering net 14.

With reference to what diagrammatically illustrated in FIGS. 2 to 4, thefiltering net 14 has a porous cell structure constituted by thereplication of a base cell 21. Therefore, the part of thethree-dimensional numeral model which defines the filtering net 14 isgenerated by defining a base module, which represents the base cell 21,and by replicating such a base module to reach the shape and dimensionscorresponding, in the model, to those of the filtering net 14 or asector of the filtering net 14.

By virtue of the replication of the base module, the dimensions and theshape of the cells of the filtering net 14 are substantially identicalto one another so that the distribution of the pores corresponds to thatdesigned in design and is uniform.

The base module of the three-dimensional numerical model comprises aplurality of filiform elements which correspond to respective elongatedfiltering elements of the base cell 21. Hereinafter, the elongatedfiltering elements of the filtering net 14 are indicated with the word“filaments” (diagrammatically illustrated by lines or cylinders in FIGS.5a, 5b, 5c and 6).

The porosity is set substantially on the three-dimensional numericalmodel to obtain the required trade-off between the various needs (havinggood filtering properties; avoiding excessive back pressures;facilitating the evacuation of the residual powders from the pores atthe end of the forming procedure; obtaining a light-weight filter etc.).

The configuration of the base module, and consequently the configurationof the base cell 21, are chosen so as to optimize the capture of oil bythe filtering net 14.

The filaments 22 of the base cell 21 extend along respective axes 23,which are parallel. As shown in FIGS. 5a-5c , the axes 23 may berectilinear, curved or defined by broken lines. The axes 23 are orientedso that the filaments 22 are transversal to a mean input direction ofthe air-oil mixture in the disc 10. Such figures also show that thefilaments 22 of the cells of the filtering net 14 extend continuouslyfrom face 11 a to face 11 b, but this must not be understood aslimiting. Indeed, the height of the base cell 21 along the axes 23 maybe smaller, and the filtering net 141 could have other filteringelements in intermediate position between the faces 11 a,11 b at theends of the cells.

The cross-section of each filament 22 is substantially constant alongthe respective axis 23. Furthermore, the cross-section of the filiformelements in the three-dimensional numeral model is set equal for allfiliform elements, so that the filaments 22 have cross-sectionsidentical to one another.

As shown in FIG. 2, the filaments 22 of the base cell 21 are comprisedbetween three and six, of which at least one intermediate filament (22a) and two end filaments (22 b,22 d), arranged on opposite parts of theintermediate filament. Furthermore, by sectioning the base cell 21 withany plane P (corresponding to the plane in FIG. 2) orthogonal to theaxes 23, the traces of the axes 23 are arranged along two straight linesB and C, which are incident at the trace of the axes 23 of theintermediate filament 22 a so as to form substantially an L, or thesides of a triangle. In other words, the straight lines B and C join thetrace of each axis 23 with that of the adjacent axis 23 in the base cell21. If the number of filaments 22 of the base cell 21 is higher than orequal to four, as in the illustrated example, the straight line Bintercepts the end filament 22 b and at least one further intermediatefilament 22 c, which is arranged between the filaments 22 a and 22 b inaddition to the intermediate filament 22 a. The straight line C, on theother hand, defines the smaller side of the L or of the triangle,because it intersects only the intermediate filament 22 a and the endfilament 22 d.

The incidence angle A between the straight lines B and C is comprisedbetween approximately 90° and 160°.

Furthermore, the distance or gap S measured along the straight lines Band C between the pairs of adjacent filaments (22 a-22 d, 22 a-22 c, 22b-22 c) is equal and preferably is comprised between approximately 0.1and 3 times the maximum dimension of the cross-section of the filaments22 a,22 b,22 c,22 d.

This configuration assigns a relative position of the filaments 22,which allows to intercept the filaments with the air-oil mixture streamscaused by the filaments 22 arranged upstream along the direction of flowof mixture. The ranges assigned to the dimensional and orientationparameters of the base cell 21 allow to have a margin for defining thecorrect interaction between the streams and the obstacles, and thus theoptimal capturing efficiency as a function of the actual operativeconditions.

Again with reference to FIG. 2, measuring the dimensions D1 and D2 ofthe cross-section of the filaments 22 along any two directions which areorthogonal and lie on the plane P, each of such dimensions D1, D2 ispreferably comprised between approximately 0.1 and 0.8 mm. Also such arange of values allows to optimize the oil capturing efficiency becausethe efficiency depends on the dimensions of the obstacles that themixture encounters in the filtering net 14. In particular, the shape ofthe cross-section is circular. However, other shapes (elliptical,polygonal) could be used in order to optimize the fluid-dynamics of themixture flow about the filaments 22.

As mentioned above, the base module, which represents the base cell 21in the three-dimensional numerical model, is repeated to reach a desiredextension corresponding to that of the entire filtering net 14 or tothat of a sector or segment of the filtering net 14. The replicationoccurs along at least two transversal directions of replication.Considering the FIGS. 3 and 4, the porous structure constitutes aplurality of cells obtained by replicating the base cell 21 along adirection F and a direction G, but non necessarily rectilinear, whichare transversal and lie on the plane P.

In the case (not shown) in which the axial height of the base cell 21 issmaller than the extension of the filtering net 14, the base cell 21also would be replicated along a third direction, substantially parallelto the axes 23.

Preferably, direction F is substantially tangential or substantiallycircumferential with respect to axis 5. The base cell 21 is positionedso as to form any angle between direction F and the straight line C(i.e. an angle comprised between 0° and 180°).

In the case of FIG. 3, directions F and G are defined by respectivestraight line sheaves, which form an incidence angle comprised betweenapproximately 30° and 150°. In this case, the replication of the basecell 21 occupies only a sector of the filtering net 14. The porousstructure of the remaining part of the filtering net is defined by arotation of a predetermined angular pitch about axis 5 of such a sector.

In the case of FIG. 4, on the other hand, figure F is defined byconcentric circles, the centre of which coincides with the intersectionof the axis 5 with the plane P. Direction G, on the other hand, isdefined by a sheave of curves generated by a base curve (preferably aradial straight line) repeated with a determined angular pitch about theaforesaid centre.

With this configuration of axial-symmetric type, the size of the poreincreases as the diameter of the disc 10 increases. Thus, the oil canexit the disc 10 more easily from the radially outermost parts. In theradially innermost parts, on the other hand, the obstacles defined bythe filaments 22 are closer and tend to increase the air-oil separationeffect.

The replication pitch of the base cell 21 along the two directions F andG is established so as to position the cells according to theadvancement direction of the mixture flow (considered as mean directionor as directions in localized zones) and to optimize the interaction ofthe streams of the mixture with the obstacles defined by the filaments22.

For example, the distance or gap T between two subsequent cells alongdirection F (FIG. 3) is comprised between approximately 0.1 and 3 timesthe maximum dimension of the cross-section of the filaments 22 (thereplication pitch along direction F is equal to the sum of the gap T andof the dimension of the filament 22 along the same direction F).

More in general, the pitch and the other replication parameters allow tooptimize the geometry of the porous structure of the filtering net 14according to the operating conditions of the disc 10, i.e. to optimizethe position of the obstacles against which the mixture strikes as afunction of the direction of the local mixture flow itself. Furthermore,the porous structure may be designed in dedicated manner to satisfyspecific requirements of a given application, while the geometries ofthe filtering nets of the prior art cannot be optimized or adaptedexcept for a restricted number of parameters.

With reference again to figures from 5 a to 5 c, the orientation of theaxes 23 in space depends on the specific application and is set so as tooptimize the inclination angle of the obstacles against which themixture strikes, as a function of the inlet direction of the mixtureinto the disc 10.

Typically, if the flow of mixture enters into the disc 10 insubstantially radial direction, the axes 23 of the base cell 21 areparallel to the axis 5 (FIG. 5b ).

If the flow of the mixture enters inclined with respect to the radialdirection, when cross-sectioning the disc 10 with a diametrical sectionplane (FIGS. 5a, 5c and 6) the axes 23 of the filaments 22 form aninclination angle Z comprised between a few degrees and 50° with respectto axis 5 at the face 11 a.

Independently from the inclination angle with respect to axis 5 and thepossible curvature of the axes 23, the parallel configuration of thefilaments 22, starting from face 11 a, does not obstruct theintroduction of the mixture and helps the radial evacuation of the oiloutwards while working. Furthermore, the parallel configuration of thefilaments 22 considerably simplifies the evacuation operations of theresidual powders at the end of the forming procedure. Such advantagesare amplified by the fact that the filaments 22 extend continuously fromface 11 a to face 11 b, without intermediate filtering elements.According to variants (not shown), the filtering net 14 could compriseadditional filtering grids which are substantially flat, extend alongthe faces 11 a and/or 11 b and are substantially made in one piece withthe other elements of the disc 10.

With reference to FIGS. 6, 8 and 9, as regards the frame 20, the lattercomprises an outer peripheral structure or element 31, which is arrangedalong the surface 12 and defines at least one window 32 to allow the oilto exit radially towards the portion 16. Similarly, the frame 20comprises an inner peripheral structure or element 33, which is arrangedalong the surface 13 and defines at least one window 34 to allow the airto flow into the axial cavity 7 through the openings 18.

In particular, the elements 31 and 33 comprises respective pairs ofrings 35 and 36, arranged along the circular edges of the disc 10; andrespective pluralities of crosspieces 37,38, which are spaced apartalong the outer circumference and the inner circumference of the disc10, respectively. The crosspieces 37 join the rings to one another andseparate the windows from one another 32. Similarly, the crosspieces 38join the rings 36 to one another and separate the windows 34 from oneanother.

The rings 35,36 are also called “hoops” and have the function ofsupporting the inertia loads caused by rotation. In other words, therings 35,36 stiffen the disc 10 so as to limit the deformations of thefiltering net 14 under load, and consequently guarantee the structuralintegrity of the disc 10.

The cross-section of the rings 35 and 36 may be a triangle, a trapezium,a circle, an ellipsis or a rectangle, and has an axial dimension S1 anda radial dimension S2, with S1 and S2 each included betweenapproximately 1 and 5 mm. The shape and dimensions of the cross-sectionof the rings 35,36 are set so as to optimize the passage area and thepath of the oil flows at the outer circumference and of the air flows atthe inner circumference, respectively. Furthermore, the shape anddimensions of the cross-section of the rings 35,36 are set so as tointegrate the rings 35,36 with the position and the orientation of thefilaments 22.

As shown in FIGS. 8 and 9, the windows 32 and 34 are engaged preferablyby respective grids 39, 40, which are made in one piece with thefiltering net 14 and the frame 20. The grids 39,40 substantially extendalong the surface 12 and the surface 13, respectively, and consist ofelongated or filiform elements (not shown), which are filtering, i.e.have a cross-section with dimensions substantially equal to thoseindicated for the filaments 22 (D1,D2).

The elongated filtering elements of the grids 39,40 are positioned so asto intersect the filaments 22 which end at the windows 32,34, so as tosupport the ends of such filaments 22. The elongated filtering elementsof each grid 39,40 are parallel to one another.

In addition to the elements 31 and 33, in general the frame 20 comprisesat least one element arranged in radial intermediate position betweenthe surfaces 12 and 13.

In particular, the frame 20 comprises a plurality of elements defined bybeams 44, which extend in either circumferential or tangential directionwith respect to axis 5 and, together with the rings 35 and 36, stiffenthe disc 10 and support the inertia loads caused by rotation forguaranteeing the structural integrity of the disc 10 and limit thedeformations of the filtering net 14 under load.

As shown in the cross section in FIG. 6, the beams 44 also have thefunction of supporting the filaments 22. In particular, the beams 44 arearranged substantially along the faces 11 a,11 b and support the ends ofthe filaments 22 of the filtering net 14. In particular, the beams 44have a flat cross-section, equal to one another, so as to definerespective baffles which tend to guide the mean flow, or macro-flow, ofthe air-oil mixture which passes through the faces 11 a,11 b. Thecross-sections of the beams 44 are elongated along directions N which,considering any diametrical section plane, are parallel to each other,and preferably are not orthogonal to the faces 11 a,11 b. In particular,the inclination angle M of the direction N with respect to axis 5 isequal to the inclination angle Z of the filaments 22. In the variantshown in the cross section in FIG. 7, on the other hand, the inclinationangles M and Z are different.

The inclination angle M is comprised between approximately 0° and 75°and is set so as to obtain the correct direction of the mixture withrespect to the filtering net 14 as a function of the operatingconditions of the filter 8.

In particular, each beam 44 has two sides 46,47, one radially outer andthe other radially inner, which are substantially parallel and definethe direction N. Furthermore, each beam 44 has two bases 48,49 ofsmaller extension with respect to the sides 46,47: the base 48 axiallyfaces outwards and does not support any other filament 22; the base 49,on the other hand, axially faces the inside of the disc 10. Withreference to FIG. 9, the inclination angle M for the beams 44 arrangedalong the face 11 b is such to orient the bases 49 towards the axis 5;on the other hand, the inclination angle M for the beams 44 arrangedalong the face 11 a is such to orient the bases 49 towards the surface12. Thus, the baffles defined by the beams 44 obstruct the centripetalradial motion of the mixture and help the centrifugal motion of the oilfacilitating draining off from the filter 8.

As shown in FIG. 6, each beam 44, in a radial direction, issubstantially arranged between two series of filaments 22′ and 22″ andis substantially aligned with a series of filaments 22′″. The base 49directly supports the end portions 50 of the filaments 22′″, i.e. theportions 50 are butted to the base 49, so that the filaments 22′″ extendstarting from the base 49 towards the opposite axial face of the disc10.

The sides 46,47 support the end portions of the filaments 22′ and 22″,respectively, by means of bridges 53 which are transversal to the endsof the filaments 22 and to the sides 46,47. The bridges 53 allow toobtain an optimal trade-off between weight and filtering features of thefiltering net 14. Furthermore, the joining system exploits to themaximum the supporting potentiality of the beams 44 because it uses boththe base 49 of each beam 44 and its sides 46,47 for joining groups offilaments 22 to the beam 44 itself.

When the inclination angles Z and M are different, as shown in the FIG.7, one of the sides 46,47 of each beam 44 directly supports thefilaments 22″, without bridges 53, while the other of the sides 46,47 isprovided with bridges 53.

The cross-section of the beam 44 may be circular, elliptical,trapezoidal, rectangular and is set so as to optimize the localfluid-dynamic conditions of the mixture. In the case of elongatedcross-section, orthogonally to direction N the dimension T2 of each beamis the same order of size as the dimensions of the filaments 22, i.e. iscomprised between approximately 0.1 mm and 1 mm; parallel to direction Nthe dimension T1 is comprised between approximately 1 mm and 15 mm (FIG.7).

Again with reference to FIGS. 8 and 9, the frame further comprises pairsof elements 60,61, which extend in substantially radial directionthrough the filtering net 14. Preferably, the elements 60,61 arearranged along the faces 11 a, 11 b, so as to intersect the beams 44,and preferably have an axial dimension substantially equal to that ofthe beams 44. The elements 60,61 have the double function oftransferring the centrifugal loads from the beams 44 towards the rings35,36 and of acting as radial blades for expelling the oil and managingthe fluid-dynamic field of motion of the mixture inside the disc 10.

The pairs of elements 60 are spaced apart about the axis 5 by a constantangle, so that each pair of elements 60 is arranged, in circumferentialdirection, between two adjacent sectors of the filtering net 14.Furthermore, the pair of elements 60 extend radially for the entire disc10 and, advantageously, end radially at the crosspieces 37,38, so thateach pair of elements 60 form, together with a crosspiece 37 and acrosspiece 38, a respective rectangular annular frame 62 (FIG. 8).

The pairs of elements 61 are intercalated between the pairs of elements60 about the axis 5. In particular, each pair of elements 61 is arrangedangularly at the half between two adjacent frames 62. The pairs ofelements 61 extend only in an outer portion of the disc and end radiallyoutwards at the rings 35, and radially inwards at respective crosspieces64 which are parallel to axis 5 and are arranged in intermediate radialposition between the surfaces 12 and 13. Thus, each pair of elements 61and the corresponding crosspiece 64 form a respective U-shaped frame 65(FIG. 9).

As the other components of the frame 20, the elements 60,61 also stiffenthe disc 10 to limit deformations under load and to guarantee thestructural integrity of the disc 10.

Furthermore, the elements 60,61 have a flat cross-section equal to oneanother, and elongated in direction parallel to axis 5, so as to definerespective radial blades, as mentioned above, to improve the oilexpulsion radially outwards. The cross-section may be shaped/dimensionedas to adjust the fluid-dynamic conditions of the mixture inside the disc10. The elements 60,61 may generate a so-called impeller effect tooptimize the local speed of the mixture and improve the interaction ofthe mixture itself with the filaments 22. Preferably, the elements 60,61have respective pluralities of ridges 63, which protrude in directionparallel to axis 5 towards the inside of the filtering net 14 withrespect to the remaining part of the elements 60,61 and, for eachelement 60,61 are radially spaced apart.

In the illustrated example, the cross-sections of the elements 60,61 arerectangular with smaller base (in tangential direction) comprisedbetween approximately 0.1 and 1 mm and larger base (in axial direction)comprised between approximately 1 and 10 mm. However, the cross-sectioncould be different, e.g. circular or elliptical, to optimize the localfluid-dynamic conditions.

The frames 62,65 define respective openings corresponding to the passagesection for mixing in tangential direction. Preferably, such openingsare engaged by grids 66,67, which are made in one piece with thefiltering net 14 and the frame 20, are substantially flat and extend inradial direction.

The grids 66,67 are constituted by elongated or filiform elements (notshown) which are filtering, i.e. which define obstacles for separatingthe oil-air phases of the mixture. In other words, the elongatedfiltering elements of the grids 66,67 has a cross-section of dimensionssubstantially equal to the values D1 and D2 of the filaments 22. Theelongated filtering elements of the grids 66,67 are arranged inpositions such as to intersect the filaments 22 which extend through theopenings of the frames 62,65. In this manner, the elongated filteringelements of the grids 66,67 are joined to such filaments 22 andcooperate with the frame 20 in the support of the filtering net 14. Asthe grids 39 and 40, the elongated filtering elements of the grids 66,67are parallel to one another.

With reference to FIG. 8, the frame 20 comprises a bushing 70, whichextends from the face 11 a of the face 11 b and defines a cylindricalseat 71 parallel to the axis 5. The bushing 70 defines an interfaceelement for coupling fastening pins, fastening pins or similar devices,which allow to pack and/or couple the various discs 10 axially, thuspreventing relative rotations between the various discs 10 andtransmitting the sliding friction from each disc 10 to the rest of thefilter 8.

From the above, it is apparent that the disc 10 integrates, in a singlepiece, a blading and a metallic filtering net and thus allows to improvethe air-oil separation and/or reduce the loss of pressure. Inparticular, the frame 20 may be shaped so as to guide the path of themixture according to the orientation of the axes 23 of the filaments 22to maximize separation efficacy. In other words, some elements of theframe 20 may be designed and dimensioned so as to perform afluid-dynamic function of the air-oil mixture in addition to astiffening and a supporting function of the filtering net because theelements are arranged in radial intermediate position between thesurfaces 12 and 13, where the air-oil mixture passes, and are shaped asbaffles or blades.

Furthermore, the solid, massive elements of the frame 20 may replace thecage 11 with advantages in terms of weight and of construction andassembly ease, because they integrate interface elements with the othercomponents of the filter 8.

As mentioned above, the position, shape and dimensions of the structuralelements which constitute the frame 20 can be configured as a functionof the configuration of the filtering net 14 and the operatingconditions.

At the same time, the position and dimensions of the obstacles of thefiltering net 14 can be configured, within given limits, so as to makemore or less close zones or zones with obstacles appropriatelyorientated as a function of specific operating conditions.

Being made by means of layer by layer technologies, the disc 10 isbalanced and may be designed so as to be relatively light, by virtue ofthe fact that the porous structure is set in desired, predeterminedmanner by means of a three-dimensional cell model. Furthermore, the disc10 has a porous structure and constant quality, independently from theshape complexity.

Other advantages are thus apparent from the above-described features.

It is finally apparent that changes and variations can be made to thefiltering net 14 described and illustrated without departing from thescope of protection of the accompanying claims.

In particular, the frame 20 and the filtering net 14 could be used toform filter portions, e.g. to form sectors, which are then assembled toeach other and/or used in fields other than aeronautics, e.g. in rotaryseparators in industrial systems or in turbines for marine propulsionand in electric generators.

The invention claimed is:
 1. A filter comprising: a disc-shapedfiltering body, wherein the disc-shaped filtering body comprises a firstaxial face, a second axial face and an axis extending from the firstaxial face to the second axial face; wherein the disc-shaped filteringbody further comprises an inner surface located at the innercircumference of the disc-shaped filtering body and an outer surfacelocated at the outer circumference of the disc-shaped filtering body;wherein the disc-shaped filtering body further comprises a framedisposed between the inner surface and the outer surface, wherein theframe comprises a plurality of beams, wherein each beam comprises a topsurface, a bottom surface and a solid body extending from the topsurface to the bottom surface, and wherein each beam is angled such thatit slopes downwardly in a direction from the inner surface toward theouter surface such that the top surface of each beam is directed towardthe inner surface while the bottom surface of each beam is directedtoward the outer surface in a manner such that the solid body extends ina direction from the inner surface toward the outer surface; and whereinthe disc-shaped filtering body further comprises a filtering net whichis defined by filaments defining a plurality of pores therebetween,wherein the filtering net is supported by the frame and wherein thefiltering net is made in one piece with the frame.
 2. The filteraccording to claim 1, wherein each of said plurality of beams have thesame cross-section, and wherein each of said plurality of beams iselongated in a direction parallel to said axis and has two substantiallyparallel faces each having an inclination angle of between approximately0° and 75° with respect to said axis.
 3. The filter according to claim1, wherein each of said plurality of beams has two substantiallyparallel faces and supports the ends of three series of filaments,wherein two of said three series of filaments are supported,respectively, by said two substantially parallel faces, and wherein thethird of said three series of filaments is substantially aligned withone of said plurality of beams.
 4. The filter according to claim 3,further comprising a plurality of transversal bridges, which connect theends of at least one of said series of filaments to the correspondingone of said two substantially parallel face.
 5. The filter according toclaim 1, wherein said frame comprises: an outer peripheral elementarranged along said outer surface and defining at least one firstwindow, and an inner peripheral element arranged along said innersurface and defining at least one second window.
 6. The filter accordingto claim 5, wherein said at least one first window and said at least onesecond window are fitted with respective grids, wherein said respectivegrids are each formed by a plurality of elongated filtering elements,and wherein the plurality of elongated filtering elements have a portionthat is joined to a portion of the ends of said filaments.